Publication DE 100 61 293 A1 shows a method and a device for improving the efficiency of an asynchronous motor. In this case, three-phase power is supplied in order to activate the motor. A direct voltage and a direct current are measured and used to determine an estimated active power. Conclusions regarding the loading of the asynchronous motor can be drawn from the estimated active power.
An estimated torque-producing current value is also determined and compared with the actual torque-producing current value. In addition, the difference between the actual and the estimated torque-producing current value is determined. The estimated active power is changed on the basis of this determined difference. The three-phase power supplied to the asynchronous motor can be changed on this basis.
A method and a device for increasing the efficiency of an electric motor are also known from publication DE 10 2005 036 802 B3.
Another conventional device for operating a three-phase asynchronous motor is described in publication DE 10 2008 018 625 A1.
An example of a three-phase current controller is also shown in “Soft-Started Induction Motor Modeling and Heating issues for Different Starting Profiles Using a Flux Linkage ABC Frame of Reference”, Mark G. Solveson, Behrooz Mirafzal, and Nabeel A. O. Demerdash, in IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 42, NO. 4, JULY/AUGUST 2006.